This research focuses on oxidative modification of proteins. The resulting covalent modifications have been implicated in important physiologic and pathologic processes. Determination of the actual roles of oxidative modification in these processes requires the identification of specific proteins which are susceptible to modification and the mapping of the sites of modification in those proteins. During this year, we placed increased emphasis on the potential physiological functions of oxidative modification of proteins. The modifications being studied in most detail are those of the metal-catalyzed oxidation of iron-responsive protein-2. We showed previously that the protein is rapidly oxidatively modified in vivo when cells become iron-sufficient. The modified protein is then ubiquitinylated and degraded by the proteosome. We have studied recombinant full-length iron-responsive protein-2 and a recombinant, smaller portion of the protein, attempting to reconstitute the metal-catalyzed oxidation in vitro. We have now been able to find conditions which reproducibly yield oxidatively modified recombinant peptide. The oxidative modification occurs in a cysteine residue, with the first product likely being dehydrocysteine. This is further oxidized to aminomalonic acid. These oxidation products are presumably recognized by a specific ubiquitin ligation and then by the proteasome. We showed previously that the mouse model of the neurodegenerative disease ataxia-telangiectasia, ATM, is characterized by oxidative stress and oxidative modification of macromolecules. This year we completed the initial phase of a collaborative study to investigate the feasibility of pharmacological intervention to reduce oxidative stress and oxidative damage in this mouse model.